Electrodeposition as a coating application method involves the deposition onto a conductive substrate of a film-forming composition under the influence of an applied electrical potential. Electrodeposition has gained popularity in the coatings industry because it provides higher paint utilization, outstanding corrosion resistance, and low environmental contamination as compared with non-electrophoretic coating methods. Both cationic and anionic electrodeposition processes are used commercially.
There are a number of applications in which it is desired to control the gloss of a coating layer applied by electrodeposition while retaining or improving other coating properties, such as corrosion resistance. Desirable electrodeposited coatings having a low gloss level that is retained after exterior exposure have, however, been very hard to prepare. The addition of traditional flatting agents such as silicas and alumina silicates to electrodepositable coating compositions can produce the desired gloss levels initially, but the finishes discolor and chalk quickly upon exposure to the elements. Furthermore, traditional flatting agents are often much more dense than other coating composition components and will settle in the electrocoat baths. As a result, continuous recirculation must be employed to maintain paint homogeneity, even when the bath is not in use. The need for continuous recirculation can lead to higher capital equipment costs, higher maintenance costs, and higher energy costs.
It is therefore highly desirable to provide anionic electrodepositable coating compositions that address at least some of the deficiencies discussed above.